J-band variability of M dwarfs in the WFCAM Transit Survey

N. T. Goulding, J. R. Barnes, D.J. Pinfield, G. Kovacs, J. Birkby, S. Hodgkin, S. Catalan, B. Sipocz, H.R.A. Jones, C. del Burgo, S.V. Jeffers, S. Nefs, M. -C. Galvez-Ortiz, E. L. Martin

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Abstract

We present an analysis of the photometric variability of M dwarfs in the Wide Field Camera (WFCAM) Transit Survey. Although periodic light-curve variability in low mass stars is generally dominated by photospheric star spot activity, M dwarf variability in the J band has not been as thoroughly investigated as at visible wavelengths. Spectral type estimates for a sample of over 200 000 objects are made using spectral type-colour relations, and over 9600 dwarfs (J <17) with spectral types later than K7 were found. The light curves of the late-type sample are searched for periodicity using a Lomb-Scargle periodogram analysis. A total of 68 periodic variable M dwarfs are found in the sample with periods ranging from 0.16 to 90.33 d, with amplitudes in the range of similar to 0.009 to similar to 0.115 in the J band. We simulate active M dwarfs with a range of latitude-independent spot coverages and estimate a periodically variable fraction of 1-3 per cent for stars where spots cover more than 10 per cent of the star's surface. Our simulated spot distributions indicate that operating in the J band, where spot contrast ratios are minimized, enables variability in only the most active of stars to be detected. These findings affirm the benefits of using the J band for planetary transit searches compared to visible bands. We also serendipitously find a Delta J > 0.2 mag flaring event from an M4V star in our sample.

Original languageEnglish
Pages (from-to)3358-3373
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume427
Issue number4
DOIs
Publication statusPublished - Dec 2012

Keywords

  • stars: activity
  • stars: late type
  • stars: starspots
  • stars: variables: general
  • SKY SURVEY DATA
  • LOW-MASS STARS
  • SCALE MAGNETIC TOPOLOGIES
  • FIELD M-DWARFS
  • MONITOR PROJECT
  • MAIN-SEQUENCE
  • TIME-SERIES
  • SPACED DATA
  • COOL STARS
  • MID-M

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